The present disclosure generally relates to semiconductor devices, and particularly to semiconductor structures including multi-thickness conductive metallic nitride layers providing multiple work functions, and methods of manufacturing the same.
In complementary metal oxide semiconductor (CMOS) replacement gate integration schemes, multiple work functions are needed in gate electrodes in order to provide optimal threshold voltages to various field effect transistors. Because satisfactory operation of p-type field effect transistors (PFETs) and n-type field effect transistors (NFETs) in a CMOS circuit require gate electrodes having work functions that differ by at least 300 mV˜400 mV, a variety of work function metals are used in order to obtain a set of desired workfunctions on various CMOS devices in replacement gate integration schemes. However, such work function metals tend not to provide sufficiently low resistivity, thereby requiring deposition of additional fill metals with low resistivity. Thus, typical replacement gate electrodes include a stack of about 4-5 layers of different metals. With the scaling of semiconductor devices to the 22 nm node and the 15 nm node, filling narrow gate cavities employing a stack of different conductive material layers becomes more challenging.